This application claims the priority of European Patent Application Serial No. 99 102 637.8, filed Feb. 12, 1999, the subject matter of which is incorporated herein by reference.
The present invention relates, in general, to a paint spraying apparatus, and more particularly to a paint spraying apparatus of a type including a conveyor unit having an endless conveyor belt, trained over at least two belt-reversing rollers, for transporting an article to be coated, and at least one cleaning unit operatively connected to the conveyor unit for wiping a surface of the conveyor belt clean.
In a paint spraying apparatus of this type, the conveyor belt is relatively wide and has no openings or breakthroughs. The application of paint, lacquer, enamel or like coats onto the articles is realized by controlled spay guns arranged above the conveyor unit. For sake of simplicity, the following description will refer to paint only, but it will be understood by persons skilled in the art, that other coats such as lacquer or enamel generally follow the concepts outlined here and thus are considered to be covered by this disclosure. As a consequence of the configuration of the conveyor belt, it is inevitable that gaps between successive articles will also be sprayed, thereby depositing a coat of paint on the conveyor belt. Therefore, the outside of the conveyor belt must be thoroughly cleaned immediately after removing the articles from the conveyor unit.
In order to keep the loss of paint to a minimum, it has been proposed to provide a paint spraying apparatus which is equipped with a paint recovery unit that essentially includes a cylinder in axis-parallel disposition to the rollers of the conveyor unit. The cylinder is driven in a same direction of rotation as the neighboring roller of the conveyor unit so that contacting surfaces of the roller and the cylinder move in opposite directions. Paint separated by the cylinder from the conveyor belt is subsequently scraped off the cylinder by strippers and collected in a gutter which is configured with a downward slope so that paint can flow by way of gravity into a subjacent tank when the paint is sufficiently fluid, or discharged laterally from the gutter by a mechanically operated slide. This, however, necessarily requires accumulation of a certain quantity of paint in the gutter so that some paint will dry on, thereby adversely affecting the recovery operation. In addition, as the cylinder extends across the entire width of the conveyor belt, the spray painting apparatus is complicated in structure and rather cost-intensive. Moreover, it is nearly impossible to sufficiently clean the conveyor belt when paint of relatively high viscosity, i.e. viscous or pasty paint, is processed.
Another conventional paint spraying apparatus uses for the transport of articles being coated a conveyor unit which is comprised of several extremely narrow conveyor belts. In the area of the spray guns, excess paint, so-called overspray, is received by a wiping belt which extends perpendicular to the conveyor unit and is cleaned by a stripping device. This paint spraying apparatus also suffers shortcomings as paint will deposit on the narrow transport belts, which therefore have to be cleaned.
It is thus an object of the present invention to provide an improved paint spraying apparatus, obviating the afore-stated drawbacks.
In particular, it is an object of the present invention to provide an improved paint spraying apparatus which is simple in structure and cost-efficient while yet realizes a sufficient cleaning of the conveyor belt, even when highly viscous or pasty as well as fast drying paints are processed.
These objects, and others which will become apparent hereinafter, are attained in accordance with the present invention by providing a conveyor unit having an endless conveyor belt, trained over at least two drums, for transporting an article to be coated, and at least one cleaning unit operatively connected to the conveyor unit for wiping a surface of the conveyor belt clean, with the cleaning unit including an endless wiping belt extending obliquely relative to the conveyor belt and so operated as to run at a higher speed than the conveyor belt when contacting the conveyor belt.
In accordance with the present invention, the wiping belt forms a main part of the cleaning device and has a width which is substantially smaller than the width of the conveyor belt. Guidance of the wiping belt requires few and simple components. As a consequence of the slanted disposition of the wiping belt relative to the rotation axes of the drums of the conveyor belt and the operation of the wiping belt at a higher speed than the conveyor belt, a speed component is realized which is directed to the outer edge of the wiping belt so that paint is removed from the conveyor belt by the continuously revolving wiping belt and laterally discharged in a quickest possible manner, without requiring the provision of an additional gutter or additional mechanical slides. The crossing pattern between the travel directions of the conveyor belt and the wiping belt results in an abrasive action which allows processing of even highly viscous paints while still accomplishing a thorough and superior cleaning of the conveyor belt, and yet is small enough so not to cause attrition of the conveyor belt and of the wiping belt.
According to another feature of the present invention, the wiping belt of the cleaning unit is associated to a drum for the conveyor belt and/or a sliding shoe deflecting the conveyor belt. Thus, a fixed abutment for the wiping belt is realized that promotes the cleaning effect as a deflection of the conveyor belt is thereby prevented. The overall configuration can be further minimized when this drum is the trailing one of the two drums as viewed in traveling direction of the upper strand of the conveyor unit, because the conveyor belt can then be cleaned immediately and easily after removing the spray-coated article as the paint sprayed onto the conveyor belt has not yet dried to a substantial extent. Also, the association of the wiping belt to the drum of the conveyor belt trailing provides also good access to the wiping belt to carry out maintenance and cleaning works.
Suitably, the wiping belt has a side edge which extends at an acute angle of approximately 10 degrees, preferably 7 degrees, to an axis which runs perpendicular to a side edge of the conveyor belt. This angular disposition ensures in conjunction with a suitably selected relatively high traveling speed of the wiping belt a secure removal of paint from the conveyor belt while still keeping the width of the wiping belt comparably small. To prevent a lateral run-off of paint from the wiping belt, it is suitable to incline the wiping belt by a small angle of e.g. 2 to 3 degrees with respect to the horizontal so that the outer conveyor belt distal side edge of the wiping belt is disposed at an elevated level with respect to the inner conveyor belt proximal side edge. A deflection of the conveyor belt contacting upper strand of the wiping belt relative to the conveyor belt can be avoided by supporting the upper strand of the wiping belt on a stationary carrier plate. The carrier plate is formed in its surface, which confronts the upper strand of the wiping belt, with a groove which extends in spaced and parallel disposition to the boundary edges of the upper strand and has a variable distance to the side edges of the carrier plate as a result of the slanted orientation of the groove with respect to the longitudinal edges of the carrier plate. The groove may extend on both sides of the vertical projection of the rotation axis of the pertaining belt-reversing roller, so that the upper strand of the wiping belt slightly embraces the conveyor belt being cleaned, thereby realizing a flat engagement between the wiping belt and the conveyor belt.
According to yet another feature of the present invention, the wiping belt is trained over a trailing first roller, when viewed in moving direction of the upper strand, and over a second roller which is positioned underneath the first roller, with a doctor blade positioned between the first and second rollers for removing paint, scraped off the conveyor belt, from the wiping belt. The downward travel of the wiping belt via the second roller is advantageous as the wiping belt projects beyond the conveyor belt only insignificantly, and gravity can be exploited to enhance the scrape-off action on the wiping belt. This action can be further reinforced when the second roller is in offset disposition with respect to the trailing first roller in the direction to a leading third roller, and when providing the doctor blade of single piece configuration with a V-shaped profile, with the pointed end disposed in front, when viewed in traveling direction of the wiping belt. In this manner, paint converging in the center of the wiping belt can then be directly conducted into a collecting tank under the action of gravity, without requiring any additional structural components.
According to another embodiment of the present invention, the conveyor belt and the wiping belt may travel in horizontal direction, i.e. the drums of the conveyor belt and the rollers of the wiping belt are supported on horizontal axes, with the wiping belt suitably positioned underneath the trailing roller. It is, however, also conceivable to position the conveyor belt in a vertical disposition, with the drums supported on horizontal axes, whereby the wiping belt is configured in correspondence to the previous embodiments. Suitably, the roller associated to the wiping belt extends within the respective projection of the outer contour of the wiping belt.